Image forming devices that form color images by superposing images in a plurality of colors formed respectively by a plurality of process units have conventionally performed misregistration correction to adjust color registration. An example of misregistration correction is a process of forming a registration mark in each color, acquiring the amount of offset between the mark of a reference color and the mark of an adjustment color, and adjusting the position of the adjustment color based on a correction value corresponding to the amount of offset.
Various documents have been published on adjusting images, such as the misregistration correction described above. One image forming device known in the art employs a method of counting the total number of sheets discharged from the device over time and of forming registration marks for adjusting registration when the total number of discharged sheets reaches a prescribed number pre-stored on the device (see Japanese Patent Application Publication No. 2013-125108).